Multiplexed optical transition method and multiplexed optical transmitter

ABSTRACT

A multiplexed optical transmitter according to this invention comprises first spreader which code-spreads first data stream of electrical signal by first spreading-code, first frequency-converter which converts a frequency of the code-spread first data stream into first frequency, and first electrical-optical converter which converts the first data stream into first optical carrier of first optical signal having a predetermined optical wavelength. Furthermore, the multiplexed optical transmitter comprises second spreader which code-spreads second data stream of electrical signal by second spreading-code, second frequency-converter which converts a frequency of the code-spread second data stream into second frequency, and second electrical-optical converter which converts the second data stream into second optical carrier of second optical signal having the predetermined optical wavelength. Then, an optical coupler couples the first optical signal and the second optical signal for generating a multiplexed optical signal having the first optical carrier and the second optical carrier.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an optical transmission methodand an optical transmitter which use code-division multiplexing andoptical carrier multiplexing.

[0002] Conventionally, in order to realizing large-scale transmission,optical transmitters using both of the time-division multiplexing andthe wavelength-division multiplexing, or using the optical sub-carriermultiplexing, which superimposes many data signals into opticalcarriers, are proposed.

[0003]FIG. 2 shows a schematic diagram of a conventional multiplexedoptical transmission system using both of the time-division multiplexingand the wavelength-division multiplexing.

[0004] In the FIG. 2, each of Data_(—1), . . . , Data_(—M) is a datastream which is time-division multiplexed, and inputted into opticaltransmitters (:TX) 210 _(—1), . . . , 210 _(—M) at the transmitter side,respectively.

[0005] The optical transmitters 210 _(—1), . . . , 210 _(—M) havedifferent oscillation wavelengths λ₁, . . . , λ_(M), and they outputoptical signals modulated based on the inputted data streams Data_(—1),. . . , Data_(—M) respectively.

[0006] The modulated optical signals outputted from the opticaltransmitter 210 _(—1), . . . , 210 _(—M) and having differentwavelengths each other, are coupled by a coupler (:MUX) 220.Consequently, a wavelength-division multiplexed optical signal isgenerated and transmitted to the receiver side via optical fibertransmission lines (:fiber) 230.

[0007] At the receiver side, the wavelength-division multiplexed opticalsignal is separated into elements of wavelengths λ₁, . . . , λ_(M) by ade-mixer (:DE-MUX)240, and the elements are inputted into opticalreceivers (:RX) 250 _(—1), . . . , 250 _(—M) respectively.

[0008] At the optical receivers 250 _(—1), . . . , 250 _(—M), the datastreams Data_(—1), . . . , Data_(—M) are reproduced form the inputtedelements, respectively.

[0009] Also in the case of optical sub-carrier multiplexing, opticaltransmitters for the optical sub-carrier multiplexing differs from thetransmitters of the FIG. 2 in that the transmitters for the opticalsub-carrier multiplexing superimposes data into optical carriers ofoptical signals. However, the transmitters for the optical sub-carriermultiplexing and the transmitters of the FIG. 2 overlap about thesystems use plural optical transmitters having different oscillationwavelengths each other and using a coupler for wavelength-divisionmultiplexing.

[0010] In the case of the above-mentioned conventional transmissionsystems, when oscillation wavelengths (:optical frequencies) λ₁, . . . ,λ_(M) of the optical transmitters 210 _(—1), . . . , 210 _(—M) areapproximated or accorded each other, interference between the signalscause beat noises deteriorating transmission quality of the systems.

[0011] Then, in order to keep the transmission quality, the conventionaloptical transmitters need some components having wavelength stabilizingfunction and wavelength supervisory function. And the components causeincreasing of the optical transmitter cost.

[0012] Furthermore, in order to prevent the interference, thetransmitters of the systems can't have narrow separations between theoscillation wavelengths.

[0013] Thus the conventional systems restrict a number of signalwavelengths a regular capacity, or arrangements of selectable signalwavelengths.

SUMMARY OF THE INVENTION

[0014] In view of the foregoing, an object of the present invention isto realize a multiplexed optical transition system for large-scaletransmission without increasing of optical transmitters cost.

[0015] A multiplexed optical transmitter according to this inventioncomprises first spreader which code-spreads first data stream ofelectrical signal by first spreading-code, first frequency-converterwhich converts a frequency of the code-spread first data stream intofirst frequency, and first electrical-optical converter which convertsthe first data stream into first optical carrier of first optical signalhaving a predetermined optical wavelength.

[0016] Furthermore, the multiplexed optical transmitter comprises secondspreader which code-spreads second data stream of electrical signal bysecond spreading-code, second frequency-converter which converts afrequency of the code-spread second data stream into second frequency,and second electrical-optical converter which converts the second datastream into second optical carrier of second optical signal having thepredetermined optical wavelength.

[0017] Then, an optical coupler couples the first optical signal and thesecond optical signal for generating a multiplexed optical signal havingthe first optical carrier and the second optical carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a schematic diagram disclosing a multiplexed opticaltransmission system as first.

[0019]FIG. 2 is a schematic diagram disclosing a conventionalmultiplexed optical transmission system.

[0020]FIG. 3 is a block diagram disclosing optical transmitters 110_(—1), . . . , 110 _(—M) of the first embodiment.

[0021]FIG. 4 is a block diagram disclosing an optical receiver 140 ofthe first.

[0022]FIG. 5 is a schematic diagram showing the signal distributionstates of the input data on each step of the transmitter side.

[0023]FIG. 6 is a diagram showing the signal distribution states ofinput data on the optical signal, which are outputted from the opticaltransmitters 110 _(—1), . . . , 110 _(—M) of the first embodiment.

[0024]FIG. 7 is a schematic diagram showing a construction of amultiplexed optical transmission system of the second embodiment.

[0025]FIG. 8 is a block diagram showing a construction of the opticaltransmitter 710 of the second embodiment.

[0026]FIG. 9 is a block diagram showing a construction of the opticalreceiver 720 of the second embodiment.

[0027]FIG. 10 is a diagram showing the signal distribution states ofinput data on the optical signal, which are outputted from the opticaltransmission unit 711 _(—1), . . . , 711 _(—M) of the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028]FIG. 1 shows a construction of first embodiment of the invention.

[0029] A multiplexed optical transmission system of the first embodimentis comprised of M optical transmitters (:TX) 110 _(—1), . . . , 110_(—M), a beam splitter (:Splitter) 120, optical fiber transmission lines(:fiber)130, and an optical receiver (:RX) 140.

[0030] Each of the optical transmitters (:TX) 110 _(—1), . . . , 110_(—M) is supplied with data streams of the electrical signal Data_(—1),. . . , Data_(—M) respectively.

[0031] The beam splitter 120 works as optical coupler and multiplexesoptical signals outputted from the optical transmitters 110 _(—1), . . ., 110 _(—M) respectively.

[0032] The optical fiber transmission lines 130 are connected to thebeam splitter 120.

[0033] The optical receiver (:RX) 140 extracts the data stream of theelectrical signal Data_(—1), . . . , Data_(—M) from an optical signalinputted via the optical fiber transmission lines 130.

[0034] In FIG. 1, each of the optical transmitters 110 _(—1), . . . ,110 _(—M) is an optical transmitter outputting an optical signal havingfixed optical wavelength λ₀. And, the optical transmitters 110 _(—1), .. . , 110 _(—M) uses spreading-codes L₁, . . . , L_(N) and frequenciesf₁, . . . , f_(M) for multiplexing.

[0035] Detailed constructions of the optical transmitter 110 _(—1), . .. , 110 _(—M) are shown in a block diagram of FIG. 3.

[0036] The optical transmitters 110 _(—1), . . . , 110 _(—M)substantially have the same construction.

[0037] Therefore, only the optical transmitter 110 _(—1) is explaineddetailed construction and the other optical transmitters 110 _(—2), . .. , 110 _(—M) are explained only different parts from the opticaltransmitter 110 _(—1).

[0038] First, the construction of the optical transmitter 100 _(—1) isexplained as representation of the optical transmitters 110 _(—1), . . ., 110 _(—M).

[0039] The optical transmitter 110 _(—1) is comprised of a dataprocessing circuit (:S/P convert) 301, a spreader (L₁) 302 _(—1), . . ., a spreader (L_(N)) 302 _(—N), a multiplexer 303, an up-converter (f₁)304 _(—1), and an electrical-optical converter (λ₀) 305.

[0040] When the data stream of the electrical signal Data_(—1) isinputted into the data processing circuit (:S/P convert) 301, theelectrical signal Data_(—1) is serial-parallel converted and dividedinto N data streams of the electrical signal.

[0041] Each of the N data streams of the electrical signal isrespectively inputted into the spreader (L₁) 302 _(—1), . . . , thespreader (L_(N)) 302 _(—N), which code-spread the inputted data streamby using the spreading-codes L₁, . . . , L_(N) respectively.

[0042] The code-spread N data streams of the electrical signal aremultiplexed in the multiplier 303, and then, the multiplexed electricalsignal is inputted in the up-converter (f₁) 304 _(—1), which is afrequency-converter.

[0043] In the up-converter (f₁) 304 _(—1), the multiplexed electricalsignal is up-converted, namely frequency-converted as a multiplexedelectrical signal having frequency of the f₁.

[0044] Then, the multiplexed electrical signal is inputted into theelectrical-optical converter (λ₀) 305.

[0045] The electrical-optical converter (λ₀) 305 has an LD oscillatorwhich radiates laser beam having the fixed optical wavelength λ₀, and byusing direct modulation method or an external modulator, outputs anoptical signal having optical wavelength λ₀ and superimposed themultiplexing signal as optical carrier.

[0046]FIG. 5 is a schematic diagram showing the signal distributionstates of the input data on each step of the transmitter side.

[0047] As it is shown in the diagram, at the spreader (L_(x)) 302 _(—x),a digital signal is code-spread based on spreading-code Lx in a band ofintermediate frequency f_(B). Then, at the up-converter (f_(x)) 304_(—x), the signal is converted into a code-spread signal based on thespreading-code L_(x) in a band of frequency fx.

[0048] After that, the code-spread signal is converted into a opticalsignal by the electrical-optical converter (λ₀) 305. Consequently, thedigital data is included in an optical signal having optical wavelengthλ₀ as distributing in a band of optical carrier fx.

[0049] Also in the optical transmitters 110 _(—2), . . . , 110 _(—M),which the data streams of the electrical signals Data_(—2), . . . ,Data_(—M) are inputted respectively, processing almost equivalent to theoptical transmitter 110 _(—1) is performed.

[0050] However, regarding the optical transmitters 110 _(—2), . . . ,110 _(—M), each component differs at the point of frequency-convertinginto multiplexed signals having frequency of the signal f₂, . . . ,frequency of the signal f_(M) by using up-converter (f₂) 304 _(—2), . .. , up-converter (f_(M)) 304 _(—M) respectively.

[0051] Then, it is as follows when the process of electrical-opticalconverting at each of the data streams of the electrical signalData_(—1), . . . , Data_(—M) is generalized.

[0052] Each of data stream Data_(—m) among the electrical data streamsData_(—1), . . . , Data_(—M) is serial-parallel converted by the dataprocessing circuit (:S/P convert) into m_(—1) _(^(st)) , . . . m_(—N)_(^(th)) data streams respectively, wherein M is an integer of 2 ormore, m is an integer of 1≦m≦M, and N is an integer of 1 or more.

[0053] Then, each of m_(—n) _(^(th)) data stream among the m_(—1)_(^(st)) , . . . , m_(—N) _(^(th)) data streams is code-spread byspreader (L_(n)) having spreading-code L_(n) respectively, wherein n isan integer of 1≦n≦N.

[0054] After that, the m_(—1) _(^(st)) , .., m_(—N) _(^(th)) datastreams are multiplexed by a multiplier, and converted frequency of themultiplexed data stream by up-converter (f_(m)) into frequency f_(m).

[0055] Finally, at an electrical-optical converter (λ₀), the multiplexeddata stream including the m_(—1) _(^(st)) , . . . , m_(—N) _(^(th)) datastreams is superimposed on an optical signal having an opticalwavelength λ₀ as optical carriers.

[0056] Consequently, each of the m_(—n) _(^(th)) data stream isconverted into m_(—n) _(^(th)) optical carrier of m_(—n) _(^(th))optical signal having the same optical wavelength λ₀.

[0057] Furthermore, by using FIG. 6, signal distribution state of eachoptical signal outputted from the optical transmitters 110 _(—1), . . ., 110 _(—M) is explained.

[0058] As previously explained using the FIG. 5, information aboutpredetermined data stream is distributed on a band of predeterminedoptical carrier f_(x), which is included in an optical signal having theoptical wavelength λ₀, as a state of code-spread by predeterminedspreading-code L_(x).

[0059] For example, in the case of an optical signal having an opticalwavelength λ₀ which is outputted from the optical transmitter 110 _(—1),the data stream Data_(—1) is distributed on a band of optical carrierf₁, as states of code-spread by predetermined spreading-codes L₁, . . ., L_(N) respectively.

[0060] Similarly, in the case of an optical signal outputted from theoptical transmitter 110 _(—2), the data stream Data_(—2) is distributedon a band of optical carrier f₂, as states of code-spread bypredetermined spreading-codes L₁, . . . , L_(N) respectively.

[0061] Then, as the result of coupling them by the beam splitter 120, amultiplexed optical signal, which includes the data streams Data_(—1), .. . , Data_(—M) distributed on bands of optical carriers f₁, . . . ,f_(M) as states of code-spread by predetermined spreading-codes L₁, . .. , L_(N) respectively, is generated.

[0062] The multiplexed optical signal is inputted into an opticalreceiver RX via optical fiber transmission lines 130.

[0063] Based on the spreading-codes L₁, . . . , L_(N) and thefrequencies f₁, . . . , f_(M), the optical receiver RX de-multiplexesthe data streams of the electrical signal Data_(—1), . . . , Data_(—M)and outputs them.

[0064] Detailed construction of an optical receiver (:RX) 140 isexplained in FIG. 4 as a block diagram.

[0065] The optical receiver 140 comprises an optical-electricalconverter 401, and data converters 400 _(—1), . . . , 400 _(—M)connecting the optical-electrical converter 401 respectively.

[0066] In the FIG. 4, the data converters 400 _(—1), . . . , 400 _(—M)substantially have the same construction.

[0067] Therefore, only the data converter 400 _(—1) is explaineddetailed construction and the other data converters 400 _(—2), . . . ,400 _(—M) are explained only different parts from the data converter 400_(—1).

[0068] First, the construction of the data converter 400 _(—1) isexplained as representation of the data converters 400 _(—1), . . . ,400 _(—M).

[0069] The data converter 400 _(—1) is comprised of a band pass filter(:BPF) (f₁) 402 _(—1), a down-converter (1/f₁) 403 _(—1), de-spreaders(L₁) 404 _(—1), . . . , de-spreaders (L_(N)) 404 _(—N), and a dataprocessing circuit (:P/S convert) 405.

[0070] When the multiplexed optical signal λ₀ is inputted into theoptical-electrical converter 401, the multiplexed optical signal λ₀ isconverted into an electrical signal.

[0071] At this point, a optical intensity fluctuation of the multiplexedoptical signal λ₀ corresponds to the multiplexed signal superimposed asthe optical carriers.

[0072] Consequently, the optical-electrical converter 401 can easilyconvert the multiplexed optical signal into the multiplexed signal of anelectrical signal.

[0073] Then, the electrical signal is inputted to the data converters400 _(—1), . . . , 400 _(—M) respectively.

[0074] In the data converter 400 _(—1), the inputted electrical signalis filtered by a band pass filter (f₁) 402 _(—1). As a result, elementsof the frequency f₁ band are only extracted from the inputted electricalsignal.

[0075] Then, the elements of the frequency f₁ band arefrequency-converted into frequency 1/f₁ by a down-converter (1/f₁) 403_(—1), or a frequency-converter.

[0076] The signal converted into the frequency 1/f₁ contains multiplexedN data streams which are code-spread at the optical transmitter 110_(—1) by the spreading-codes L₁, . . . , L_(N) respectively.

[0077] Each of the N data streams is de-spread by de-spreaders (L₁) 404_(—1), . . . , (L_(N))404 _(—N) using the spreading-codes L₁, . . . ,L_(N) respectively.

[0078] Finally, the N data streams are parallel-serial converted by adata processing circuit (:P/S convert) 405. So, the data stream of theelectrical signal Data_(—1), which is inputted in the opticaltransmitter 110 _(—1), is reproduced.

[0079] In the reproducing process, signal distribution states of anysteps are reverse process of the multiplexing process at the opticaltransmitter 110 _(—1), which has been explained by using the FIG. 5previously. So, detailed explanation of the process is omitted.

[0080] Also in the data converters 400 _(—2), . . . , 400 _(—M), processof reproducing almost equivalent to the data converter 400 _(—1) isperformed.

[0081] However, regarding the data converters 400 _(—2), . . . , 400_(—M), each component differs at the points of filtering the inputtedelectrical signal by band pass filters (f₂) 402 _(—2), . . . , (f_(M))402 _(—M) for extracting elements of the frequency f₂, . . . , f_(M)bands respectively, and frequency-converting the elements of thefrequency f₂, . . . , f_(M) bands into frequencies 1/f₂, . . . , 1/f_(M)by using down-converters (1/f₂)403 _(—2), . . . , (1/f_(M))403 _(—M),respectively.

[0082] Then, the data streams Data_(—2), . . . , Data_(—M) arereproduced like the process at the data converter 400 _(—1).

[0083] According to the multiplexed optical transmission system of thefirst embodiment, the optical signal is modulated based on aspectrum-spread signal which is generated by code-division multiplexing.

[0084] Consequently, since narrow spectrum noises with high powerdensity like beat noises between signal-wavelengths are not recognizedas correlation codes, it does not make deterioration of transmissionquality.

[0085] The optical transmitters 110 _(—1), . . . , 110 _(—M) of thefirst embodiment output optical signals having identical opticalwavelength.

[0086] Then, each of the data streams is code-spread by predeterminedspreading-code and frequency-converted into predetermined frequency.

[0087] Thereafter, the data streams are superimposed in optical carriersof optical signals having the same wavelength, and are multiplexed.

[0088] So, the optical signals outputted from the optical transmitters110 _(—1), . . . , 110 _(—M) can be coupled by using inexpensive powercoupler/splitter like the beam splitter 120.

[0089] Consequently, the embodiment realizes reducing a cost oftransmission system.

[0090] Furthermore, selecting the spreading-codes of the code-spreadingand the frequency of the frequency-converting as each of the datastreams is assigned at least one of spreading-code or frequencydifferent each other, “the number of spreading-codes x the number offrequencies” data streams can be multiplexing-transmitted by using oneoptical wavelength.

[0091] Then, a second embodiment of the invention will be explained byreferring FIG. 7, which discloses a construction of the embodiment.

[0092]FIG. 7 is a schematic diagram showing a construction of amultiplexed optical transmission system comprising optical transmitters(:TX) 710 and 770, optical receivers (:RX) 720 and 760, a beam splitter(:Splitter) 730 and 750, and optical fiber transmission lines (:fiber)740.

[0093] And, the system carries out bi-directional transmittingdifferently the first embodiment.

[0094] The optical transmitter 710 and the optical receiver 760 are usedfor signal transmission to the right side from the left side in thediagram, and the optical transmitter 770 and optical receiver 720 areused for signal transmission to the left side from the right side.

[0095] Both are substantially symmetrical construction. Therefore, wewill explain only about the relations between the optical transmitter710 and the optical receiver 760, and the explanation of the other sideis omitted.

[0096] In FIG. 7, the optical transmitter 710 comprises opticaltransmission units 711 _(—1), . . . , 711 _(—M).

[0097] Each of the optical transmission units 711 _(—1), . . . , 711_(—M) outputs an optical signal having an optical wavelength λ₀, thetransmitter 710 multiplexes signals by using frequencies of the signalf₁, . . . , f_(N) and spreading-codes L₁, . . . , L_(M).

[0098] By using a block diagram of FIG. 8, detailed construction of theoptical transmitter 710 will be explained. Incidentally, the opticaltransmission units 711 _(—1), . . . ,711 _(—M) of the opticaltransmitter 710 are basically the identical construction. In the FIG. 8,only the construction of the optical transmission unit 711 _(—1) isexplained detailedly. Then, remaining optical transmission units 711_(—2), . . . ,711 _(—M) are only explained constructions difference fromthe optical transmission unit 711 _(—1), and the same constructions areomitted.

[0099] First, representing the optical transmission units 711 _(—1), . .. ,711 _(—M), a construction of the optical transmission unit 711 _(—1)will be explained.

[0100] The optical transmission unit 711 _(—1) comprises a dataprocessing circuit (:S/P convert) 801, N spreaders (L₁) 802 _(—1), anup-converters (f₁) 804 _(—1), . . . ,(f_(N)) 804 _(—N), a multiplier803, and electrical-optical converter (λ₀) 805.

[0101] When a data stream of electrical signal Data_(—1) is inputtedinto the data processing circuit (:S/P convert) 801, the stream isconverted serial-parallel. As a result, the stream is divided into Ndifferent data streams of electrical signal.

[0102] Each of the N data streams is inputted into corresponding Nspreaders (L₁) 802 _(—1) respectively, which code-spread the datastreams using a spread code L₁.

[0103] The code-spread N data streams are respectively inputted into theup-converters (f₁) 804 _(—1), . . . ,(f_(N)) 804 _(—N) forfrequency-converting, which up-convert frequencies of the code-spread Ndata streams into f₁, . . . ,f_(N) respectively.

[0104] The frequency-converted N data streams are multiplexed by themultiplier 803 and inputted into the electrical-optical converter (λ₀)805 which generates an optical signal having an optical wavelength λ₀.Consequently, the multiplexed N data streams are superimposed on theoptical signal as an optical carrier.

[0105] Also in the optical transmission units 711 _(—2), . . . , 711_(—M), which the data streams of the electrical signals Data_(—2), . . ., Data_(—M) are inputted respectively, processing almost equivalent tothe optical transmission unit 711 _(—1) is performed.

[0106] However, regarding the optical transmission units 711 _(—2), . .. , 711 _(—M), each component differs at the point of code-spreading byinputted into N spreaders (L₂) , . . . , (L_(M)) respectively.

[0107] Then, it is as follows when the process of electrical-opticalconverting at each of the data streams of the electrical signalData_(—1), . . . , Data_(—M) is generalized.

[0108] Each of data stream Data, among the electrical data streamsData_(—1), . . . , Data_(—M) is serial-parallel converted by the dataprocessing circuit (:S/P convert) into m_(—1) _(^(st)) , . . . m_(—N)_(^(th)) data streams respectively, wherein M is an integer of 2 ormore, m is an integer of 1≦m≦M, and N is an integer of 1 or more.

[0109] Then, each of m_(—n) _(^(th)) data stream among the m_(—1)_(^(st)) , . . . , m_(—N) _(^(th)) data streams is code-spread byspreader (L_(m)) having spreading-code L_(m) respectively, wherein n isan integer of 1≦n≦N.

[0110] After that, the m_(—1) _(^(st)) , . . . , m_(—N) _(^(th)) datastreams are multiplexed by a multiplier, and converted frequency of themultiplexed data stream by up-converter (f_(n)) 804 _(—n) into frequencyf_(n).

[0111] Finally, at an electrical-optical converter (λ₀) 805, themultiplexed data stream including the m_(—1) _(^(st)) , . . . , m_(—N)_(^(th)) data streams is superimposed on an optical signal having anoptical wavelength λ₀ as optical carriers.

[0112] Consequently, each of the m_(—n) _(^(th)) data stream isconverted into m_(—n) _(^(th)) optical carrier of m_(—n) _(^(th))optical signal having the same optical wavelength λ₀.

[0113] Furthermore, by using FIG. 10, signal distribution state of eachoptical signal outputted from the optical transmission units 711 _(—1),. . . , 711 _(—M) is explained.

[0114] For example, in the case of an optical signal having an opticalwavelength λ₀ which is outputted from the transmission unit 711 _(—1),the data stream Data_(—1) is distributed on bands of optical carriersf₁, . . . , f_(N) respectively, as state of code-spread by aspreading-code L₁.

[0115] Similarly, in the case of an optical signal outputted from theoptical transmission unit 711 _(—2), the data stream Data_(—2) isdistributed on bands of optical carriers f₁, . . . , f_(N) respectively,as state of code-spread by a spreading-code L₂.

[0116] Then, as the result of coupling them by the beam splitter 730, amultiplexed optical signal, which includes the data streams Data_(—1), .. . , Data_(—M) distributed on bands of optical carriers f₁, . . . ,f_(N) as states of code-spread by predetermined spreading-codes L₁, . .. , L_(M) respectively, is generated.

[0117] The multiplexed optical signal is inputted into an opticalreceiver 760 via optical fiber transmission lines 730 and a beamsplitter 750.

[0118] Based on the spreading-codes L₁, . . . , L_(M) and thefrequencies f₁, . . . , f_(N), the optical receiver 760 de-multiplexesthe data streams of the electrical signal Data_(—1), . . . , Data_(—M)and outputs them.

[0119] Detailed construction of an optical receiver 760 is explained inFIG. 9 as a block diagram.

[0120] The optical receiver 760 comprises an optical-electricalconverter 901, band pass filters (:BPF) (f₁) 902 _(—1), . . . , (f_(N))902 _(—N) connecting the optical-electrical converter 901 respectively,down-converters (1/f₁) 903 _(—1), . . . ,(1/f_(N)) 903 _(—N) connectingeach of the band pass filters (:BPF) (f₁) 902 _(—1), . . . , (f_(N)) 902_(—N) respectively, and data converters 900 _(—1), . . . , 900 _(—M)connecting the down-converters (1/f₁) 903 _(—1), . . . ,(1/f_(N)) 903_(—N) reciprocally.

[0121] In the FIG. 9, the data converters 900 _(—1), . . . , 900 _(—M)substantially have the same construction.

[0122] Therefore, only the data converter 900 _(—1) is explaineddetailed construction and the other data converters 900 _(—2), . . . ,900 _(—M) are explained only different parts from the data converter 900_(—1).

[0123] First, the construction of the data converter 900 _(—1) isexplained as representation of the data converters 900 _(—1), . . . ,900 _(—M).

[0124] The data converter 900 _(—1) is comprised of N de-spreaders (L₁)904 _(—1) arranged in parallel, and a data processing circuit (:P/Sconvert) 905 connecting the N de-spreaders (Li) 904 _(—1).

[0125] When the multiplexed optical signal λ₀ is inputted into theoptical-electrical converter 901, the multiplexed optical signal λ₀ isconverted into an electrical signal.

[0126] At this point, a optical intensity fluctuation of the multiplexedoptical signal λ₀ corresponds to the multiplexed signal superimposed asthe optical carriers.

[0127] Consequently, the optical-electrical converter 901 can easilyconvert the multiplexed optical signal into the multiplexed signal of anelectrical signal.

[0128] Then, the electrical signal is inputted to the band pass filters(f₁) 902 _(—1), . . . , (f_(N)) 902 _(—N) arranged in parallel,respectively.

[0129] And, each of elements of the frequency f₁, . . . , f_(N) bands isextracted by the band pass filters (f₁) 902 _(—1), . . . , (f_(N)) 902_(—N) respectively.

[0130] Then, each of the elements of the frequency f₁, . . . , f_(N)bands is frequency-converted into frequencies 1/f₁, . . . , 1/f_(N) bydown-converters (1/f₁) 903 _(—1), . . . , (1/f_(N)) 903 _(—N)respectively.

[0131] The signals converted into the frequencies 1/f₁, . . . , 1/f_(N)contain N data streams which are code-spread at the optical transmissionunit 711 _(—1) by the spreading-code L₁.

[0132] Therefore, in the data converter 900 _(—1), each of the N datastreams is de-spread by the N de-spreaders (L₁) 904 _(—1) using thespreading-code L₁ respectively.

[0133] Finally, the N data streams are parallel-serial converted by adata processing circuit (:P/S convert) 905. So, the data stream of theelectrical signal Data_(—1), which is inputted in the opticaltransmitter 710, is reproduced.

[0134] Also in the data converters 900 _(—2), . . . , 900 _(—M), processof reproducing almost equivalent to the data converter 900 _(—1) isperformed.

[0135] However, regarding the data converters 900 _(—2), . . . , 900_(—M), each component differs at the points of de-spreading byde-spreaders (L₂) 904 _(—2), . . . , (L_(M)) 904 _(—M) using thespreading-codes L₂, . . . , L_(M) respectively.

[0136] Then, the data streams Data_(—2), . . . , Data_(—M) arereproduced like the process at the data converter 900 _(—1).

[0137] According to the multiplexed optical transmission system of thesecond embodiment, like the first embodiment, the optical signal ismodulated based on a spectrum-spread signal which is generated bycode-division multiplexing.

[0138] Consequently, since narrow spectrum noises with high powerdensity like beat noises between signal-wavelengths are not recognizedas correlation codes, it does not make deterioration of transmissionquality.

[0139] In the case of conventional bi-directional optical transmissionsystems, in order to prevent interference between wavelengths, thesystems need to use different wavelength for each direction.

[0140] Or when using the wavelength in both directions, in case onetransmitter is used, transmitter of another side needs to be stopped.

[0141] Moreover, common coupler has directional characteristic. So, onconventional bi-directional optical transmission systems, eachtransmission direction is need couplers for optical transmitter and foroptical receiver, respectively.

[0142] By contrast, because of the embodiment uses wide band for signaltransmitting and code-division multiplexed signal superimposed on anoptical signal. For this reason, since there is few influence of theinterference, there is no necessity of preparing a special function likethe conventional bi-directional optical transmission systems.

[0143] Moreover, the same as the first embodiment, the second embodimentuses optical signals using identical optical wavelength.

[0144] Then, each of the data streams is code-spread by predeterminedspreading-code and frequency-converted into predetermined frequency.

[0145] Thereafter, the data streams are superimposed in optical carriersof optical signals having the same wavelength, and are multiplexed.

[0146] So, the optical signals can be coupled or separated by usinginexpensive power coupler/splitter.

[0147] As shown in the FIG. 7, the optical transmitter 710 and theoptical receiver 720 can share the beam splitter 730, and the opticaltransmitter 770 and the optical receiver 760 can share the beam splitter750.

[0148] Consequently, the embodiment realizes reducing a cost oftransmission system further.

[0149] In the first and second embodiments, the data processing circuit(:S/P convert) serial-parallel converts one data stream into N datastreams. However, the invention does not necessarily need suchserial-parallel converting.

[0150] As an intelligible example, in the above-mentioned constructions,the case of N=1 corresponds to multiplexing M data streams withoutserial-parallel converting.

[0151] Furthermore, according to inputting a respectively different datastream into a total of “M×N” spreaders prepared in the first, . . . ,M^(th) optical transmitters 110 _(—1), . . . , 110 _(—M), the total of“M×N” data streams can be multiplexed.

[0152] Also by these cases, each data streams superimposed into theoptical carrier differ in spreading-code and/or frequency offrequency-converting mutually.

[0153] Therefore, using predetermined filtering and de-spreading at theoptical receiver can reproduce each of the data streams.

[0154] In addition, unlike the first embodiment, the second embodimenthas the construction that the first, . . . , M^(th) data streams arecollectively inputted into single optical transmitter, i.e., the opticaltransmitter 710 or 770. And, the optical transmission units 711 _(—1), .. . , 711 _(—M) are explained as components of the single opticaltransmitter.

[0155] However, the second embodiment may change the opticaltransmission units 711 _(—1), . . . , 711 _(—M) as individual opticaltransmitters.

[0156] Furthermore, the outputs of the optical transmitters don't haveto be multiplexed at once.

[0157] Then, the outputs can be multiplexed selectively at couplerslocated in optional points of the optical transmission lines.

[0158] Similarly, the first and second embodiment have the constructionthat the first, . . . , M^(th) data streams are collectively outputtedfrom single optical receiver, i.e., the optical receiver 140, 720 or760. And, they may change the optical receivers as individual opticaltransmitters corresponding to the data streams.

[0159] Then, like the optical transmitters, the data streams can bede-multiplexed selectively at splitters located in optional points ofthe optical transmission lines.

[0160] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof.

[0161] The present embodiments are therefore to be considered in allrespects as illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed is:
 1. A method for multiplexed optical transition, themethod comprising the steps of: code-spreading first data stream ofelectrical signal by first spreading-code, and converting a frequency ofthe code-spread first data stream into first frequency; converting thefirst data stream into first optical carrier of first optical signalhaving a predetermined optical wavelength; code-spreading second datastream of electrical signal by second spreading-code, and converting afrequency of the code-spread second data stream into second frequency;converting the second data stream into second optical carrier of secondoptical signal having the predetermined optical wavelength; and couplingthe first optical signal and the second optical signal for generating amultiplexed optical signal having the first optical carrier and thesecond optical carrier.
 2. The method according to claim 1, wherein thefirst spreading-code is different from the second spreading-code, or thefirst frequency is different from the second frequency.
 3. A method formultiplexed optical transition, the method comprising the steps of:serial-parallel converting each of m data stream among first, . . .M^(th) data streams of electrical signal into m_(—1) _(^(st)) , . . .m_(—N) _(^(th)) data streams respectively; code-spreading each of m_(—n)_(^(th)) data stream among the m_(—1) _(^(st)) , . . . , m_(—N) _(^(th))data streams by n^(th) spreading-code, and converting a frequency of thecode-spread m_(—n) _(^(th)) data stream into m^(th) frequencyrespectively; converting each of the m_(—n) _(^(th)) data stream intom_(—n) _(^(th)) optical carrier of m_(—n) _(^(th)) optical signal havingthe same optical wavelength respectively; and coupling each of them_(—n) _(^(th)) optical signal for generating a multiplexed opticalsignal having the m_(—n) _(^(th)) optical carrier, wherein M is aninteger of 2 or more, m is an integer of 1≦M≦N is an integer of 1 ormore, and n is an integer of 1≦n≦N.
 4. A method for multiplexed opticaltransition, the method comprising the steps of: serial-parallelconverting each of m data stream among first, . . . M^(th) data streamsof electrical signal into m_(—1) _(^(th)) , . . . m_(—N) _(^(th)) datastreams respectively; code-spreading each of m_(—n) _(^(th)) data streamamong the m_(—1) _(^(st)) , . . . , m_(—N) _(^(th)) data streams bym^(th) spreading-code, and converting a frequency of the code-spreadm_(—n) _(^(th)) data stream into n^(th) frequency respectively;converting each of the m_(—n) _(^(th)) data stream into m_(—n) _(^(th))optical carrier of m_(—n) _(^(th)) optical signal having the sameoptical wavelength respectively; and coupling each of the m_(—n)_(^(th)) optical signal for generating a multiplexed optical signalhaving the m_(—n) _(^(th)) optical carrier, wherein M is an integer of 2or more, m is an integer of 1≦m≦M, N is an integer of 1 or more, and nis an integer of 1≦n≦N.
 5. A multiplexed optical transmitter comprising:first spreader which code-spreads first data stream of electrical signalby first spreading-code; first frequency-converter which converts afrequency of the code-spread first data stream into first frequency;first electrical-optical converter which converts the first data streaminto first optical carrier of first optical signal having apredetermined optical wavelength; second spreader which code-spreadssecond data stream of electrical signal by second spreading-code; secondfrequency-converter which converts a frequency of the code-spread seconddata stream into second frequency; second electrical-optical converterwhich converts the second data stream into second optical carrier ofsecond optical signal having the predetermined optical wavelength; andan optical coupler which couples the first optical signal and the secondoptical signal for generating a multiplexed optical signal having thefirst optical carrier and the second optical carrier.
 6. The multiplexedoptical transmitter according to claim 5, wherein the firstspreading-code is different from the second spreading-code, or the firstfrequency is different from the second frequency.